This invention relates to methods and systems for treating livestock wastes and other organic materials, and in particular to an improved aerobic thermophilic methods and systems for treating such materials.
There are numerous ways of treating livestock waste and other organic materials to break these materials down into less objectionable, useful products. One relatively inexpensive way is to flush the waste into lagoons where the waste can be broken down by bacteria and stored until final use (typically application to the soil to increase crop production). There are two basic types of lagoons, anaerobic and aerobic. In anaerobic lagoons, anaerobic bacteria (i.e., bacteria that do not need oxygen) break down the wastes. Anaerobic lagoons are the most common, because they are simple to construct and operate. However, while modem design techniques and proper management control minimize most problems, anaerobic lagoons can be the source of objectionable odors. In aerobic lagoons, aerobic bacteria (i.e., bacteria that need oxygen) break down the wastes. These lagoons need either a very large surface area or mechanical aeration to provide adequate oxygen for the bacteria. For this reason, aerobic lagoons are less common, even though they are less likely to be the source of objectionable odors.
More recently, aerobic thermophilic treatment (also referred to as A-T treatment) has been applied to livestock wastes. A-T treatment uses aerobic biological oxidation at thermophilic (high) temperatures (approximately 55xc2x0 C.) to achieve high pollutant reductions in a relatively short time. A-T treatment requires relatively little capital investment and achieves faster processing times and reduced odor production.
The methods and apparatus of the present invention relate to improvements in A-T treatment of livestock wastes and other organic materials. A-T treatment typically involves passing air through a reactor containing the waste or other organic material. Oxygen from the air is absorbed by the material in the reactor, promoting the microbial breakdown of the material in the reactor. According to the improvements of the present invention, at least a portion of the air that has passed through the organic matter in the reactor is captured and recycled through the organic material in the reactor. The inventor has discovered that a major loss of heat in A-T treatment systems is due to the evaporation of water into the air passing through the material in the reactor. However, once the air has passed through the material, it has been heated and humidified and retains as much as 85% of the available oxygen. Thus by recycling at least some of the air, and reducing fresh air, heat loss due to evaporation can be reduced, yet sufficient oxygen remains in the air for oxygenating the material in the reactor. The resulting process and system produce excess heat that can be productively used for heating buildings, etc.
In accordance with a first alternative embodiment of this invention, the reactor is substantially enclosed, and ammonia is removed from the air that has passed through the organic matter before that air is released to the atmosphere. Escaping ammonia in prior treatment systems is responsible for some of the odor associated with waste treatment, and results in significant loss of nitrogen.
In accordance with a second alternative embodiment of this invention, ammonia is removed from the air before it is again passed through the organic matter. The removal of ammonia not only reduces odors resulting from operation and reduces loss of nitrogen, but also helps promote the aerobic bacteria in the reactor so that the reduction of the waste is faster, more efficient, and more complete.